1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a thin film transistor substrate that uses a horizontal electric field and a fabricating method thereof that simplifies the fabrication process. Also, the present invention is directed to a liquid crystal display panel employing the thin film transistor substrate and a fabricating method thereof that simplifies the fabrication process.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls the light transmittance of a liquid crystal having a dielectric anisotropy using an electric field to thereby display a picture. The LCD includes a liquid crystal display panel that displays a picture using a liquid crystal cell matrix and a driving circuit to drive the liquid crystal display panel.
Referring to FIG. 1, a related art liquid crystal display panel includes a color filter substrate 10 and a thin film transistor substrate 20 that are joined to each other with a liquid crystal 24 therebetween.
The color filter substrate 10 includes a black matrix 4, a color filter 6, and a common electrode 8 that are sequentially provided on an upper glass substrate 2. The black matrix 4 with a matrix shape on the upper glass substrate 2. The black matrix 4 divides an area of the upper glass substrate 2 into a plurality of cell areas for the color filter 6 and prevents light interference between adjacent cells and an external light reflections. The color filter 6 is provided in the cell areas defined by the black matrix 4 so as to transmit red, green and blue light. The common electrode 8 is formed from a transparent conductive layer entirely coated onto the color filter 6 and supplies a common voltage Vcom that serves as a reference voltage for driving the liquid crystal 24. Further, an over-coated layer (not shown) for smoothing the color filter 6 may be provided between the color filter 6 and the common electrode 8.
The thin film transistor substrate 20 includes a thin film transistor 18 and a pixel electrode 22 in each cell area defined by a crossing between a gate line 14 and a data line 16 on a lower glass substrate 12. The thin film transistor 18 applies a data signal from the data line 16 to the pixel electrode 22 in response to a gate signal from the gate line 14. The pixel electrode 22 uses a data signal from the thin film transistor 18 to drive the liquid crystal 24.
The liquid crystal 24 having a dielectric anisotropy is rotated in accordance with an electric field formed by a data signal on the pixel electrode 22 and a common voltage Vcom from the common electrode 8 to control light transmittance, thereby implementing a gray scale level.
Further, the liquid crystal display panel includes a spacer (not shown) for fixing a cell gap between the color filter substrate 10 and the thin film transistor substrate 20.
In a liquid crystal display panel, the color filter substrate 10 and the thin film transistor substrate 20 are fabricated by a plurality of mask processes. One mask process may include many processes such as thin film deposition (coating), cleaning, photolithography, etching, photo-resist stripping, inspection processes, etc.
Because the thin film transistor substrate includes semiconductor process that require a plurality of mask processes, it has a complicated fabricating process that results in increased cost for the liquid crystal display panel. Therefore, a thin film transistor substrate has been developed to reduce the number of mask processes.
Liquid crystal displays are largely classified into a vertical electric field and a horizontal electric field LCDs depending upon the direction of the electric field driving the liquid crystal.
A vertical electric field liquid crystal display drives a liquid crystal in a twisted nematic (TN) mode with a vertical electric field formed between a pixel electrode and a common electrode arranged opposite to each other on the upper and lower substrate. The vertical electric field liquid crystal display has an advantage of a large aperture ratio while having a drawback of a narrow viewing angle of about 90°.
The horizontal electric field liquid crystal display drives a liquid crystal in an in plane switch (IPS) mode with a horizontal electric field between the pixel electrode and the common electrode arranged in parallel to each other on the lower substrate. The horizontal electric field liquid crystal display has an advantage of a wide viewing angle of about 160°.
The thin film transistor substrate in the horizontal electric field liquid crystal display also requires a plurality of mask processes including semiconductor processes resulting in a complicated fabricating process. Therefore, in order to reduce the manufacturing cost, it is necessary to reduce the number of mask processes.